feat(gateway): render terminal tool calls as native bash code blocks on markdown platforms (#41215)

Tool-progress now shows a terminal command in a ```bash fenced block —
full command, no surrounding quotes, no label, no 40-char truncation —
instead of the noisy `terminal: "cmd…"` line, on every platform that
renders markdown code blocks (Telegram, Slack, Matrix, WhatsApp, Feishu,
Weixin, Discord). Plain-text platforms keep the compact preview line.

Gated on a new `BasePlatformAdapter.supports_code_blocks` capability
(default False) rather than a hardcoded platform list, so plugin adapters
(Discord lives in plugins/platforms/) opt in by setting the flag. Applies
to both all/new and verbose progress modes, with a safe fallback when the
command arg is missing or blank.

gateway/platforms/base.py

@@ -1792,7 +1792,14 @@ class BasePlatformAdapter(ABC):
     - Sending messages/responses
     - Handling media
     """
-    
+
+    # Whether this platform renders triple-backtick fenced code blocks (i.e.
+    # ``format_message`` translates/preserves markdown fences into a real code
+    # block).  Drives presentation choices like rendering a ``terminal`` tool
+    # call's command as a ```bash block instead of a flat preview line.
+    # Default False (plain-text platforms); markdown-rendering adapters set True.
+    supports_code_blocks: bool = False
+
     def __init__(self, config: PlatformConfig, platform: Platform):
         self.config = config
         self.platform = platform